The ability of an individual to adequately respond to environmental antigens is critical to the well-being of that individual. Although a major site of exposure to environmental antigens is the mucosal lining of the digestive tract, little is known of the effect of increasing age on the "mucosal" immune response. This application proposes the development of a murine model with which to study the effect of age on the body's antibody response to ingested antigen. Mice will be given multiple, intragastric injections of sheep red blood cells (SRBC). After 1 or 5 weeks, the mice will receive an intraperitoneal injection of SRBC and 4 days later their spleens, Peyer's patches and bone marrow will be assayed for anti-SRBC antibody producing cells. In addition, serum and saliva samples from each mouse will be assayed for anti-SRBC antibody titers. Three age groups will be used: 8-10 wk., 25-30 wk. and 12-15 mo. old mice. This model will provide new insights into the aging process involving the mucosal immune system, as well as an opportunity to examine the heretofore unexplored role of the bone marrow compartment in such a process.